The present invention relates to an internal combustion engine having a crankcase part and a cylinder receiving part which are tiltably mounted with respect to each other and particularly relates to control of the tilting.
In this type of internal combustion engine, the compression can be varied by means of the fact that the engine""s cylinder-receiving part (with associated cylinder head) can be tilted (inclined) to the side in relation to the crankcase part. To permit this, the cylinder-receiving part is mounted tiltably on the crankcase part on one side of the engine, and is connected movably to the crankcase part on the other, opposite side of the engine, by way of a tilt mechanism located there.
Internal combustion engines of the abovementioned type are already known, and in this connection reference may be made, for example, to U.S. Pat. No. 2,770,224 and SE-B-470 238.
The first of these patent specifications describes a piston engine with a fixed crankcase part, to which a cylinder-receiving engine part with associated cylinder cover is connected in an articulated manner. The combustion chamber volumes of the cylinders can be varied by tilting the cylinder-receiving engine part sideways about a longitudinal tilt axle. This tilting movement, i.e. change in the lateral inclination, is obtained by turning of an eccentric axle included in a tilt mechanism acting between the crankcase part and the cylinder-receiving engine part.
When the cylinder-receiving part (cylinder block) of an internal combustion engine, for example an in-line engine, of the abovementioned type is inclined (tilted) relative to the crankcase part, the distance between the crankshaft mounted in the crankcase part (with associated pistons linked to connecting rods) and the cylinders in the cylinder-receiving part changes. The volume of that part of the combustion chamber which lies above the respective piston""s upper boundary surface (piston top) at the upper dead centre of the piston is thereby changed. The compression ratio of the engine can thus be varied in this way, and efficiency is thereby optimized for varying loading conditions. The performance of the engine and thus also of the vehicle in question is thereby improved.
As a result of the above structural configuration of an internal combustion engine, and its principle of changing (varying) the compression in the cylinders by means of lateral tilting of the cylinder-receiving part in relation to the crankcase part of the engine, a certain amount of clearance or play arises both in the tilt axle bearing and in the various bearings of the tilt mechanism when the tilting movement in question takes place.
Since the tilt axle bearing on one side of the engine comprises a number of bearing lugs in the crankcase part, and a number of bearing lugs on the cylinder-receiving part which project into the spaces between these bearing lugs, and also a bearing axle passing through and connecting all these bearing lugs, it is necessary, for assembly technology reasons, to accept greater manufacturing tolerances, and thus greater bearing play, than it would be possible to achieve purely from the viewpoint of manufacturing technology.
This fact, together with the consideration that lubricant-free bearings ought in practice to be chosen xe2x80x94on account of small relative movements between interacting bearing components/bearing surfaces and the lack of sufficiently frequent changing of direction of forcexe2x80x94means that the bearing play is quite great, thereby causing unwanted noise, especially at high loads.
The primary object of the present invention is to design an engine operating with variable compression in such a way that the occurrence of the abovementioned bearing-related noise can be prevented or at least to a large extent obviated.
According to the present invention, the above object is achieved by the fact that the engine has the features set out herein.
Thus, the primary distinguishing feature of the internal combustion engine is that, arranged between the crankcase part and the cylinder-receiving part there are prestressing members which force these engine parts apart and work to counteract the occurrence of bearing play in the tilt axle bearing and in the tilt mechanism when compression modifying tilting movement between the cylinder-receiving part and the crankcase part occurs during running of the engine.
Developments and preferred embodiments of the subject of the invention are also described.
Because the cylinder-receiving part with its associated cylinder head and the crankcase part are kept stressed apart in the manner indicated above, when the gas forces in the cylinders occur, the effect of the bearing play can be at least largely eliminated and the resulting noise in the engine can be prevented.
The internal combustion engine can, for example, be a four-cylinder, five-cylinder or six-cylinder in-line engine with overlying camshafts mounted in the cylinder head securely connected to the cylinder-receiving part. It is possible (but not essential) for the cylinder head and the cylinder-receiving part to be fully integrated and constitute parts of one and the same monobloc piece (monobloc engine).
On one side of the engine, the cylinder-receiving part has bearing lugs for the hinge axle of the tilt bearing, and on the opposite side of the engine bearing lugs for the upper hinge axle of the tilt mechanism. The last-mentioned bearing lugs preferably constitute integral parts of the cylinder-receiving part. Arranged between the crankcase part and the upper hinge axle of the tilt mechanism there are link members which transmit the tilting movement and which serve to change the distance between the said upper hinge axle and an eccentric shaft which is mounted in the bearing lugs of the crankcase part and which constitutes the lower hinge axle of the tilt mechanism.
In a first main embodiment according to the invention, the prestressing members are arranged inside the bearing lugs of the tilt axle bearing and are intended, with their opposite ends, to press directly or indirectly in one direction against a tilt axle passing through the bearing lugs and mounted in the crankcase part, and, in the other direction, to press against a collar part fixed in relation to the cylinder-receiving part.
In this embodiment, it is also preferable for the tilt mechanism members to comprise rods like connecting rods coupled between, on the one hand, a first axle which runs through the hearing lugs connected securely to the cylinder-receiving part and, on the other hand, a second axle mounted eccentrically in the crankcase part, prestressing members being arranged in the rods and being intended, with their opposite ends, to press directly or indirectly against the first axle and the second axle, respectively, in order to generate a force stressing these two axles apart.
On that side of the second axle remote from the rod (link member) transmitting the tilting movement, prestressing members are also preferably arranged in the crankcase part which act between the crankcase part and the associated side of the second axle and are intended to exert pressure on the axle.
The prestressing members in both the bearing lugs of the tilt axle bearing and in the rods (link members) and the crankcase part can preferably comprise cylindrical spring stacks consisting of cup springs.
In a second, alternative embodiment according to the invention, in the area between the tilt axle bearing and the tilt mechanism, and inserted between the crankcase part and the cylinder-receiving part, there are prestressing members which tension these two parts apart and act between, on the one hand, a collar part rigidly connected to the crankcase part and, on the other hand, a collar part rigidly connected to the cylinder-receiving part.
The collar part rigidly connected to the cylinder-receiving part can then be a tightening screw provided with a specially designed head and serving to fix a cylinder lining support on the underside of the cylinder-receiving part.
The collar part rigidly connected to the crankcase part can for its part, for example, consist of one end of a prestressing bar screwed into the crankcase part.
In the last-mentioned embodiment, the prestressing members can expediently be powerful cylindrical screw springs tensioned between the opposing collar parts in question.
In general terms, however, as regards the prestressing members according to the invention, these can either be suitable compression springs or spring stacks, or other types of force generators, for example hydraulic force generators.
When the engine is an in-line engine and the prestressing members are arranged as in the abovementioned second main embodiment, it is preferable, for reasons of force symmetry, for the prestressing members to be placed in an axial row and distributed uniformly along the cylinder line, preferably in the areas between adjacent cylinders in the cylinder line.